Bulletin of the American Physical Society

5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan

Volume 63, Number 12

Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii

Session 2WAB: Nuclear Equation of State in Context of Neutron Star Merger Event II	Hide Abstracts
Chair: Akira Ohnishi, Yukawa Institute for Theoretical Physics, Kyoto Univesity Room: Hilton Kona 4

Tuesday, October 23, 2018 4:00PM - 4:30PM	2WAB.00001: Confronting gravitational-wave observations with modern nuclear physics constraints from chiral effective field theory Invited Speaker: Ingo Tews The correlation of the tidal polarizabilities Λ₁-Λ₂ for GW170817 is predicted by combining dense-matter equations of state (EOS) that satisfy nuclear physics constraints with the chirp mass and mass asymmetry for this event. Our models are constrained by calculations of the neutron-matter EOS using chiral effective field theory (EFT) Hamiltonians with reliable error estimates up to once or twice the nuclear saturation density. Chiral EFT is a systematic theory for nuclear forces that allows to develop consistent two- and three-nucleon interactions and enables calculations with controlled theoretical uncertainties. When using chiral EFT input up to twice saturation density, we find that GW170817 does not improve our understanding of the EOS. We contrast two distinct extrapolations to higher density, a minimal model (MM) which assumes that the EOS is a smooth function of density described by a Taylor expansion, and a more general model parameterized by the speed of sound that admits phase transitions. This allows us to identify regions in the Λ₁-Λ₂ plots that could hint at the existence of new phases of matter inside neutron stars (NSs). We predict the combined tidal polarizability of the NSs in GW170817 to be 80 ≤ Λ̃ ≤ 580 (280 ≤ Λ̃ ≤ 480 for the MM), which is smaller than the range suggested by the LIGO-Virgo data analysis. Our analysis also shows that GW170817 requires a NS with M =1.4M_⊙to have a radius 9.01.4<13.6 km (11.31.4<13.6 km for the MM).
Tuesday, October 23, 2018 4:30PM - 5:00PM	2WAB.00002: High-density symmetry energy and pion production in heavy-ion collisions Invited Speaker: Natsumi Ikeno The density dependence of the nuclear symmetry energy is a valuable information for understanding neutron rich systems such as the nuclear structure, heavy-ion collisions, neutron stars and their mergers. Especially, heavy-ion collisions are believed to be useful to investigate the symmetry energy at high densities. Since the neutron-proton ratio in the high-density region is not a direct observable, the pion ratio has been proposed to be a good probe to constrain the high-density behavior of the symmetry energy. At present, some theoretical studies have been performed by different transport models to investigate the sensitivity of pion observables in heavy-ion collisions. However, some of these results are contradicting to each other even qualitatively. Therefore, it is necessary to understand the relation between the pion ratio and the nucleon dynamics to deduce the information on the symmetry energy. In the experimental studies, Sn+Sn collisions have been performed at RIBF/RIKEN. In this presentation, we report the results for the pion production in central collisions of neutron-rich nuclei using our transport model that combines antisymmetrized molecular dynamics (AMD) and a hadronic cascade model (JAM). In our calculation, we found the mechanism how the delta resonance and pions are produced reflecting the dynamics of neutrons and protons.
Tuesday, October 23, 2018 5:00PM - 5:30PM	2WAB.00003: Probing Nuclear Equation of State with Heavy Ion Collisions Invited Speaker: Zbigniew Chajecki The equation of state (EOS) is a fundamental property of nuclear matter, important for studying the structure of systems as diverse as the atomic nucleus and neutron stars. Understanding the physics of neutron stars is becoming even more important recently because of the observation of gravitational waves from the neutron star merger. Nuclear reactions involving heavy-ion collisions in the laboratories can produce the nuclear matter similar to those contained in neutron stars. The density and momentum dependence of the EOS of asymmetric nuclear matter, especially the symmetry energy term, is widely unconstrained. Collisions of neutron-deficient and neutron-rich heavy ions studied in the laboratory already provide initial constraints on the EoS of neutron-rich matter at sub-saturation densities. Finding appropriate constraints, especially at higher densities, requires new experimental measurements as well as advances in theoretical understanding of nuclear collisions and neutron stars.We will review the latest progress in constraining the density and momentum dependence of nuclear symmetry energy and discuss their relevance to astrophysics, in particular neutron star mergers.

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Bulletin of the American Physical Society

5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan

Volume 63, Number 12

Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii

Session 2WAB: Nuclear Equation of State in Context of Neutron Star Merger Event II

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